The present invention relates to an RTK(real-time kinematic)-GPS(global positioning system) surveying system for sending and receiving a control command and correction data by using a network and a surveying server and a surveying terminal device for use in the RTK-GPS surveying system.
A kinematic positioning system is known as one of interferometric positioning systems for obtaining relative positional relationship between two observation stations with high accuracy by using a positioning satellite such as a GPS (refer to JP2002-311124A).
In this kinematic positioning system, one observation point as a known reference point and another observation point as an unknown observation point are used. The relative positional relationship between the two observation points is obtained with high accuracy by simultaneously receiving radio waves from the satellite such as a GPS with observation stations placed at both of the observation points, so as to obtain the position coordinates of the unknown observation point from the position coordinates of the known reference point with high accuracy. In this kinematic positioning system, the position coordinates are obtained by later analyzing the signals recorded at the observation points.
As an improvement of this kinematic positioning system, a real-time kinematic positioning system (hereinafter, referred to as RTK positioning system) is known.
In this RTK positioning system, one of two observation stations is placed as a fixed point at an observation point as a reference point having known position coordinates, so as to send observation data to a rover station, and the other observation station is placed as the rover station at an observation point having unknown position coordinates, so as to receive the positioning satellite signals and the observation data sent from the base station. The position coordinates of the rover station are measured in real time by receiving the positioning satellite signals and the observation data while performing an analysis process.
More particularly, in the RTK positioning system, as illustrated in FIG. 1, at first, a base station M1 is disposed at an observation point A as a reference point having known position coordinates, and also rover stations M2 are disposed at observation points B as unknown points each having unknown position coordinates. After the measurement of position coordinates is finished, the rover station M2 is moved to a next observation point (survey point) as an unknown point having unknown position coordinates as needed. The base station M1 and the rover station M2 receive the positioning satellite signals (radio waves) from a satellite Sa and the rover station M2 refers to the base station M1. At the same time, the rover station M2 performs an analysis process in real time, so as to sequentially obtain the position of observation point B as an unknown point.
In this RTK positioning system, a range in which the rover station M2 can refer to a specific base station M1 (hereinafter, referred to as a base station reference range) is a range of about 10 km in radius from the center of base station M1.
This is because, if the distance between the base station M1 and the rover station M2 is increased, the effects of the differences between the ionosphere and the troposphere at the observation point become can not be ignored, resulting in the deterioration in the measuring accuracy.
On the other hand, in order to refer to the correction data of the base station M1 by the rover station M2, it is necessary to send the correction data from the base station M1 to the rover station M2. For this sending, a device for wirelessly sending the correction data having a particular frequency from the base station M1 is used. Therefore, the base station M1 includes a sending device, for example, a transmitter Se having a frequency of about 400 MHz and an output of 10 mW for constantly sending the correction data. The rover station M2 includes a wireless receiver Sc capable of receiving the radio waves from the transmitter Se for referring to the sent correction data.
Moreover, as illustrated in FIG. 2, a satellite positioning system using a satellite positioning data server Dsb as a medium for sending and receiving data is known.
At least one rover station M2, a plurality of base stations M1, M1′ and communication devices Sx, Sy for establishing the communication between the rover station M2 and the base stations M1, M1′ are connected to the satellite positioning system via the GPS positioning data server Dsb.
In this satellite positioning system, the base stations M1, M1′ are generally fixed in positions each having known position coordinates. The base stations M1, M1′ constantly or periodically receive the radio waves from the satellite Sa, so as to obtain the correction data regarding the arrangement positions of the base stations M1, M1′.
The measured correction data is constantly or periodically sent to the GPS positioning data server Dsb from the base station M1 by the communication device. Accordingly, the base stations M1, M1′ are required to be fixed in the known positions and to communicate the correction data at high speed. Therefore, the communication device is used by a private line such as WAN constantly connected thereto.
Incidentally, the frequency to be used for sending the correction data in the case of wirelessly delivering the correction data is set such that the frequency of the base station M1 is different from the frequency of the base station M1′. This is because, if the borderlines of the wireless access range are adjacent to each other, it is difficult to distinguish the base station in the periphery of the borderline, causing miss-measurement. Also, if parts of the wireless access ranges overlap each other, interference is caused in the overlapped area. In this case, the two base stations M1, M1′ are used, but three base stations or more can be used.
As described above, if there is a plurality of base stations (for example, M1, M1′), the wireless transmitters M11 are set to different frequencies. The receiving frequency of the rover station M2 should therefore be adjusted depending on the base station to be used. Generally, M1, M1′ . . . to be used as the base station is selected by referring to a survey work plan, and the frequency of a base station to be used is found out before the survey work, so as to adjust the receiving frequency of the rover station. Accordingly, if the rover station M2 is moved to another base station (for example, M1′) reference range beyond the base station (for example, M1) reference range, it is necessary for the rover station M2 to refer to a different base station M1, M1′, . . . .
Therefore, it is disadvantageous to perform surveying work while constantly recognizing the relationship between the actual position of the own rover station M2 and the position of the base station (M1, M1′ or the like).
It is also inconvenient to select a base station, which can be used for RTK surveying and has a preferable receiving condition of the satellite Sa, from the correction data delivered from the base stations M1, M1′ . . . according to a condition such as the number of common satellites between the base station and the rover station, so as to appropriately set the receiving frequency depending on the base station selected by a measurer.
Moreover, in the case of using wireless communication, the communication is limited to one-way communication from the base stations M1, M1′ . . . to the rover station M2, so it is disadvantageous because the two-way sending and receiving of data which confirms the condition of the rover station M2 from the base station M1, for example, can not be performed.
Furthermore, in the case of using the Internet, there is a possibility of receiving access being unauthorized for use of a line.
Additionally, in the case of operating the communication via a network, it is necessary to use a static address for determining a communication partner. However, in the case of using a static IP address, the number of addresses is limited and also the cost for obtaining the IP address is very expensive. In the case of using a general provider, since a usable IP address is dynamic, an IP address is changed with each access. Therefore, the IP address has a disadvantage in that it can not be used as a static IP address for defining a partner, when connecting to a selected partner.
Since a specific ID is only required in an IP-VPN (Internet Protocol-Virtual Private Network), a specific number such as a machine's ID is used as an address to designate an access point.
Since an indirect observation method according to the public surveying operation manual using RTK-GPS (technical data of Geographical Survey Institute, A.1-No. 228 June, H12, http://psgsv.gsi.go.jp/koukyou/rtk_manual/htm/mokuji.htm) requires correction data delivery from one point of a base station to two points of rover stations, it has a disadvantage in that it can not operate by means of a cell-phone line.
Accordingly, there is a need for an RTK-GPS surveying system which can simultaneously access one base station from a plurality of rover stations while preventing illegal access without physically providing a private line and can prohibit access from a different group.